Traditionally, the synthesis of polyesters requires the use of catalysts to provide a sufficent rate of reaction to be commercially viable. Often, however, the catalysts that encourage the forward polymerization reaction also enhance the rates of degradation reactions. These degradation reactions can result in both an increase in color and a decrease in molecular weight. To minimize these unfavorable side reactions a stabilizing agent is added to the reaction mixture. Antimony compounds are well-known catalysts for polyester production. However, a potential deleterious side reaction of antimony compounds is their reduction to the zero valence state, which imparts a gray color as well as a reduction in clarity to the formed polyester. This side reaction, according to the art, is particularly exacerbated in the presence of the glycol 1,4-cyclohexanedimethanol (CHDM).
Hrach disclosed in U.S. Pat. No. 3,651,016 that polyesters could be prepared using a mixture of metallic antimony, metallic lead and metallic zinc. Lead could be replaced with a mixture of lead and tin. He very specifically pointed out the use of metallic metals. He also did not disclose the use of phosphorus compounds.
Kramer taught in 1993 (DE 4319008, WO 9401482) the use of a combination of antimony, phosphorus and germanium for the preparation of polyesters. He also disclosed that in addition to the mentioned components, the addition of tin, potassium and cobalt compounds can be used.
The Japanese patent (JP 93050533) assigned to Kuraray disclosed the use of a mixture of antimony, phosphorus and zinc for the preparation of polyesters containing 1,9-nonanediol. The patent also proposed the use of 500 ppm antimony trioxide (about 420 ppm of antimony) as part of the catalyst/stabilizer system.
The Japanese patent (JP 2155920) assigned to Mitsubishi mentioned the use of zinc in combination with antimony, titanium, tin and/or cerium.
Research Disclosure (RD 283052) disclosed the preparation of poly(ethylene 2,6-naphthalene dicarboxylate) containing 1,4-CHDM copolyesters using a combination of catalysts where Ti, Zn and Mn were mentioned.
At present, in order to improve the apparent whiteness of polyester fibers or neutral color characteristics of polyester plastics, toners can be incorporated into the polyester to mask or neutralize the yellow color.
U.S. Pat. No. 2,641,592 discloses polyesters containing dimethyl terephthalate with cobalt acetate and antimony.
U.S. Pat. No. 5,385,773 relates to the production of clear, colorless polyesters containing CHDM. This patent states that the antimony reduction reaction results in a grayish appearance in polyester synthesis, especially in the presence of CHDM. The patent discloses the absence of antimony in order to obtain the clear, colorless polyesters.
U.S. Pat. No. 4,745,174, discloses certain 1-cyano-3H-dibenz[f,ij]isoquinoline-2,7-diones which are useful as organic toners for polyester fibers and plastics.
U.S. Pat. No. 4,403,092 discloses colorants useful in the practice of this invention. However, no mention is made in the patent regarding the potential utility of the disclosed compounds as components to produce a good toner system for the polyesters of the invention.
Certain organic toner dyes have been disclosed in U.S. Pat. Nos. 5,372,864; 5,384,377; and 4,745,174. One or more of these patents disclose the use of certain organic toner dyes for use in polyesters generally.
Therefore, polyesters containing 1,4-cyclohexanedimethanol which have good color, good clarity and good mechanical properties would be particularly advantageous.